LEXICAL CHUNKS
Learning chunks of language is essential for English fluency. 
Of course, grammar and vocabulary are important. But, vocabulary - lexis - is more than individual words and the meaning of the individual words changes depending on context. Often, it is diificult to decipher the meaning of expressions taking words in isolation- phrases have to be taken a a whole - as chunks of language - LEXICAL CHUNKS. 
This is how we  develop language skills when growing up - we hear them in use, assimilate them and  then use them. These Lexical Chunks  an be fixed expressions, semi-fixed expressions, collocations, phrasal verbs and idioms. This short book gives some examples.
Unfortunately, in many schools scant attention is paid to them.